1. Technical Field
The present invention relates to an optical filter device, an optical module, and an electronic apparatus.
2. Related Art
In the past, there has been known an interference filter having reflecting films respectively disposed on surfaces of a pair of substrates so as to be opposed to each other across a predetermined gap, the surfaces being opposed to each other. Further, there is known an optical filter device having such an interference filter housed in a housing (see, e.g., JP-A-2008-70163).
The optical filter device described in JP-A-2008-70163 is provided with a package (a housing) having a plate-like pedestal and a cylindrical cap. The housing has a peripheral edge portion of the pedestal and one end portion of the cylinder of the cap connected to each other by welding or bonding, and a space for housing the interference filter is disposed between the pedestal and the cap. Further, the cap is provided with a hole disposed on the upper surface opposed to the pedestal, and the hole is provided with a window section for allowing light to pass therethrough.
Although JP-A-2008-70163 discloses (e.g., FIG. 6) the configuration in which the window section is fitted in the hole in the upper surface of the cap regarding the method of providing the window section, it fails to disclose other specific configurations. In the configuration disclosed in FIG. 6 of JP-A-2008-70163, there is a problem that it is not possible to sufficiently assure the airtightness of the seal between the window section and the hole. Thus, for example, if the inside of the package is desired to be kept at a reduced-pressure, air may enter the inside through a gap between the window section and the hole to thereby make it impossible to maintain the reduced-pressure state. Further, the probability that foreign matter such as electrically-charged particles or water particles enter the inside through, for example, the gap between the window section and the hole is also raised.